Calendar - show as busy/free option has disappeared

I used to be able to mark entries into my calendar as busy or free. The default was busy, but there was a section called "Show as" and I could choose to mark an entry as "free" so that time would still look available to others (especially when using Calendly etc).

This has disappeared. It has gone from all of my icloud calendars on my iphone and Mac.

Having searched the community advice, there are very few solutions that I can find. One solution suggested adding in a new icloud calendar and seeing if the option is available in the new calendar. It is not.

Both my iphone and Mac are runnning on the latest version of IOS.

I'm really hoping someone has a solution to this as I can't find anything sensible in the help guides and it is starting to cause me a lot of issues. I'm not sure why it suddenly disappeared.

Thanks